(i) Field of the Invention
The present invention relates to a novel 3-pyrroline-2-one derivative and a herbicidal composition containing this derivative as a herbicidally active ingredient particularly suitable for paddy fields. More specifically, it relates to a method for utilizing the 3-pyrroline-2-one derivative as the herbicidal composition for paddy fields.
(ii) Description of the Related Art
Heretofore, some 3-pyrroline derivatives having a herbicidal activity have been disclosed. For example, U.S. Pat. No. 5,006,157 has disclosed a compound represented by the formula ##STR2## as a herbicidal composition, and this pyrroline compound is extremely active when used in a paddy field and shows a wide herbicidal spectrum. However, in the case that water moves downward owing to a certain external factor, e.g., water leak, this compound tends to be seriously chemically injurious to paddy rice, and for this reason, it is difficult to use the above-mentioned compound in the paddy field.
In recent years, a highly selective herbicidal composition which is not injurious to crops and which can kill only weeds has been strongly desired. Furthermore, as the herbicidal composition for paddy fields, an effective herbicidal composition has been desired which can surely kill tough tenacious weeds such as barnyard grass (Echinochloa), bulrush (Scirpus juncoides), monochoria (Monochoria vaginalis) and water nutgrass (Cyperus serotinus). In addition, it has been strongly desired to develop a herbicidal composition which can be used at any time of from the pre-emergence of the weeds to the growing period of the emerged weeds without any restriction on a use period and which has a long duration of the effect.
Under such circumstances, in the actual paddy field, there are various external factors which have an influence on the effect and the chemically injurious action by the herbicidal composition. Examples of the external factors include the soil quality of the paddy field, weather conditions such as temperature and light, the depth of submergence, water leak, the movement of water due to inflow and outflow, and a difference of the planting depth of the rice. These factors function singly or in an intricately linked combination to have a large influence on the effect of the herbicidal composition to the weeds, the chemical injury to the crops, the stability of the effect and the like. Of these influence factors, the most important one is the water leak. In most of the paddy fields in which the water leak occurs, in practice, the use of the herbicidal composition must be noticeably restricted owing to the occurrence of the chemical injury and the fluctuation of the effect which are caused by the downward movement of water and the herbicidal composition.
Therefore, the present invention intends to provide a selective herbicidal composition which is not injurious to the rice in the paddy field, has a wide herbicidal spectrum in a low application rate, is usable in a wide period of from the pre-emergence of the weeds to the growing period of the emerged weeds, and keeps the high effect and the low chemical injury even under an external factor such as the water leak.